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Tsunoda et al. reported the synthesis of both enantiomers of AA3b, and determination of the absolute configuration of the AA3a side chain [111,112]. Their key step was the asymmetric aza-Claisen rearrangement reaction [113] of amide 129 derived from (R)-a-phenethylamine [(R)-128] (Scheme 14). The thermal 3,3-sigmatropic rearrangement proceeded to give 130 as a four di-astereomeric mixture, from which (7S, 8R)-130 and (7R, 8S)-130 were isolated as an inseparable mixture (82 : 18). Iodolactonization and subsequent deiodi-nation of 130 afforded lactone 131 of 64% ee. Hydrolysis of the lactone ring and prenylation gave 132. The D-threonine moiety 133 was introduced by Mitsunobu reaction, followed by deprotection to give 134 (64% ee). Macro-lactonization using Mukaiyama-Gerlach method [99,100] and purification provided ent-135 of ~ 100% ee, which was condensed with acid 136 to afford